Heretofore, there are widely known batteries each including a safety valve configured to open when the internal pressure of a battery exceeds a predetermined pressure to thereby promptly release internal gas to the outside of the battery. One of such safety valves is a non-recovering safety valve including a valve part configured to rupture or cleave when the valve opens and a valve surrounding part provided around this valve part, as disclosed in Patent Documents 1 to 4, for example.
As shown in FIGS. 16 to 18, for instance, a safety valve 917 is provided in a case lid 913 of a battery case constituting a battery 900. This safety valve 917 consists of a valve part 917e designed to rupture or cleave when the valve opens and a valve surrounding part 917f provided around this valve part 917e. The valve part 917e is a thin sheet formed with a V-section groove portion 917ev having a predetermined pattern. The valve surrounding part 917f has a ring shape surrounding the valve part 917e and is thicker than the valve part 917e. 
The above safety valve 917 operates to open when the internal pressure of the battery reaches a predetermined pressure (see FIGS. 19 and 20). Specifically, when the internal pressure reaches the predetermined pressure, the valve part 917e starts to rupture or cleave from the groove portion 917ev, thus releasing internal gas to the outside of the battery. At that time, the valve part 917e cleaves upward.